Carbohydrates are large organic molecules made of carbon, hydrogen and oxygen. Food forms of carbohydrates are foods rich in these types of molecules, such as pasta, bread, and candy. The name "carbohydrate" comes from the molecular formula, which can be described by the general formula Cm(H2O)n, which shows that they are "carbon and water" or "carbon hydrates". Small carbohydrates are commonly called "sugars," the biochemical term for this group of molecules being "saccharide," from the Greek word for sugar. Depending on the number of sugar units linked together, they can be classified as monosaccharides (one sugar unit), disaccharides (two sugar units), oligosaccharides (few sugars) or polysaccharides (polymeric versions of sugars—polymers). The scientific names of sugars can be identified by the suffix -ose at the end of the name (for example, fruit sugar is a monosaccharide called "fructose" and milk sugar is a disaccharide called lactose, which is composed of two monosaccharides, glucose and galactose, together). Sugars contain some of the functional groups we've discussed: Notice how the alcohol groups and monosaccharide units in the structures are linked to form a disaccharide through ether formation. Living beings use starches for different capabilities. Carbohydrates can store energy such as polysaccharides glycogen in animals or starch in plants. They additionally offer underlying help, like the polysaccharide cellulose in plants and the altered polysaccharide chitin in parasites and creatures. The sugars ribose and deoxyribose are parts of the spines of RNA and DNA, individually. Other sugars play critical roles in immune system function, cell-cell recognition, and many other biological roles.